1. Field of the Invention
This invention relates to sugar mills and more particularly to an adjustable four roll sugar mill for conveying and crushing chopped sugar cane to extract sucrose therefrom.
2. Prior Art
The production of sugar begins with the growing of sugar cane stalks in tropical or subtropical areas. The cane is harvested after a growing season of about seven months in the subtropics and after a growing season of about 12 to 22 months in the tropics. The cane stalks are harvested from the fields and transported to sugar mills nearby. The cane stalks are crushed or macerated between heavy grooved iron rolls while concurrently being sprayed with dilute juice to help extract the residual juice. Bagasse is the residue from the cane stalk after the juice has been extracted. The bagasse, is a fibrous substance which leaves the mill generally in the form of pressed mat. The bagasse is usually burned in boilers to provide energy for the sugar mill. It may also be used in the manufacture of paper and pressed boards.
The sucrose may be extracted in a series of mills. The mills are serially arranged so that the bagasse of one mill is conveyed immediately and continuously to the feed hopper of an adjacent mill. The space setting between the rolls on successive mills is reduced to extract the diminishing quantities of juice from the cane as it is passed therealong.
U.S. Pat. No. 2,783,870 shows how the mills are usually set up. In that patent, which is assigned to the assignee of the present invention, there is shown two roll stands, each consisting of three rolls: a top roll, a lower level cane or feed roll and bagasse roll. Between each mill unit is a conveyor belt arrangement. Each mill unit has a turnplate supported by a turn beam, mounted immediately beneath the top roll. This "T"-shaped member, for example, is shown in FIG. 1 of U.S. Pat. No. 3,127,831. The turnplate provides a stationary curvilinear surface over which the mat of crushed cane leaving the cane roll nip is supported and guided for passage to the nip of the bagasse roll. The rolls in a mill have "V"-shaped grooves which provide the nip which presses the cane therebetween. The rolls, in the prior art, also have chevron grooves which run generally longitudinally thereacross. The chevron grooves act as "gripping fingers" to pull the cane from the sloping supply chute into the pressure nip between the rolls. The chevron grooves reduce the amount of working surface of the rolls, thereby reducing the efficiency of the mill. Chevron grooves are shown, for example, in U.S. Pat. No. 2,442,065.
The gap between adjacent rolls needs to be adjusted from time to time because of a large mass of bagasse entering between the rolls, which must be accommodated, or because of wear on the rolls which must be compensated. One solution to this problem is shown in U.S. Pat. No. 2,316,843 where the top and bagasse rolls both pivot about a common juncture to permit adjustment in the gap between the top and feed rolls. This, however, is a complicated arrangement which does not permit a similar adjustment between the top and bagasse rolls.
Prior art mills have the anvil rolls uppermost on their frames, which location necessitated an ability to "float", because of variations in the cane volume used in the process. This required elaborate couplings because the anvil roll is generally the driven roll. The present invention places the driven anvil roll at the lowermost position without any need for adjustment or "floating" capabilities.
It is an object of the present invention to simplify the construction of sugar mill rolls.
It is a further object of the present invention to improve the efficiency of sugar mill rolls over that of the prior art.